Abstract
The cystine-glutamate transporter SLC7A11 has been implicated in chemoresistance, by supplying cystine to the cell for glutathione maintenance. In the NCI-60 cell panel, SLC7A11 expression shows negative correlation with growth inhibitory potency of geldanamycin but not with its analog 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), which differs in the C-17 substituent in that the the methoxy moiety of geldanamycin is replaced by an amino group. Structure and potency analysis classified 18 geldanamycin analogs into two subgroups, “17-O/H” (C-17 methoxy or unsubstituted) and “17-N” (C-17 amino), showing distinct SLC7A11 correlation. We used three 17-O/H analogs and four 17-N analogs to test the role of the 17-substituents in susceptibility to SLC7A11-mediated resistance. In A549 cells, which are resistant to geldanamycin and strongly express SLC7A11, inhibition of SLC7A11 by (S)-4-carboxyphenylglycine or small interfering RNA increased sensitivity to 17-O/H, but had no effect on 17-N analogs. Ectopic expression of SLC7A11 in HepG2 cells, which are sensitive to geldanamycin and express low SLC7A11, confers resistance to geldanamycin, but not to 17-AAG. Antioxidant N-acetylcysteine, a precursor for glutathione synthesis, completely suppressed cytotoxic effects of 17-O/H but had no effect on 17-N analogs, whereas the prooxidant ascorbic acid had the opposite effect. Compared with 17-AAG, geldanamycin led to significantly more intracellular reactive oxygen species (ROS) production, which was quenched by addition of N-acetylcysteine. We conclude that SLC7A11 confers resistance selectively to 17-O/H (e.g., geldanamycin) but not to 17-N (e.g., 17-AAG) analogs partly as a result of differential dependence on ROS for cytotoxicity. Distinct mechanisms could significantly affect antitumor response and organ toxicity of these compounds in vivo.
Footnotes
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This work was supported in part by National Institutes of Health research grant GM61390 from National Institute of General Medical Sciences and by the U.S. Food and Drug Administration.
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The views presented in this article do not necessarily reflect those of the US Food and Drug Administration.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.107.039644.
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ABBREVIATIONS: DTP, Developmental Therapeutics Program; NCI, National Cancer Institute; ROS, reactive oxygen species; GA, geldanamycin; 17-AAG, 17-(allylamino)-17-demethoxygeldanamycin; Hsp90, 90-kDa heat shock protein; 17-DMAG, 17-(2-dimethylaminoethyl)amino-17-demethoxygeldanamycin; SRB, sulforhodamine B; 4-S-CPG, (S)-4-carboxyphenylglycine; 17-AEP-GA, 17-(2-(pyrrolidin-1-yl)ethyl)amino-17-demethoxygeldanamycin; 17-DMAP-GA, 17-(dimethylaminopropylamino)-17-demethoxygeldanamycin; NAC, N-acetylcysteine; AsA, ascorbic acid; H2DCFDA, dichlorodihydrofluorescein diacetate; PBS, phosphate-buffered saline; MOA, mechanism of action; PCA, principal component analysis; siRNA, small interfering RNA; RT-PCR, reverse transcription-polymerase chain reaction.
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received July 9, 2007.
- Accepted September 17, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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